こればっかりは仕方ないんですよね。
いまみたいに定額データ通信とかありませんでしたしね。
まだテレホーダイ(23時から翌8時まで定額)の時代でしたので。
ISDNがちょくちょく出てきたかなってところです。

This simply couldn't be helped. There were no fixed-rate data plans like we have now. This was also the era of off-peak hour discounts (a flat rate from 11 p.m. until 8 a.m. the next day). This was right about the time that ISDNs were popping up here and there.